If you make an infinite loop with portals and sonic rainboom in air, you could feasibly change the density of the fluid with different gases, causing an infinite sonic rainboom as Dashie breaks the sound barrier for each of the different gases. The end result is a supply of Rainbow Power!!!

The forces of nature can be harnessed! And they said it was madness! Geez, wait, now that I think about it... I don't know if anyone would by a car claiming to be "Rainbow Powered"... people might get the wrong idea.